1. Field of the Invention
The present invention relates to an apparatus for heating fluid by burning liquid fuel and more particularly to improvement of or relating to an apparatus for heating fluid such as water, air or the like medium in which the amount of thermal energy generated by combustion of liquid fuel, that is, the amount of fuel which is burnt can be changed while normal combustion state is maintained. The apparatus of the invention is preferably mounted on a motorcar or like vehicle.
2. Description of the Prior Art
To facilitate understanding of the present invention conventional apparatus will be described below with reference to FIGS. 5 and 6. FIG. 5 illustrates the case where the fluid to be heated is air and FIG. 6 the case where the fluid to be heated is water. As is apparent from the drawings, the conventional apparatus is so constructed that a mechanical type fuel pump 100 (metering pump with a plunger used therefor), a combustion air blower 102, a centrifugal type fuel distributor 104 and a blower 106 for forcibly circulating air to be heated (FIG. 5) or a water pump 108 (FIG. 6) are rotationally driven by means of a single motor 110. As the motor 110 is rotated, combustion air as identified by double line marks is caused to enter the cylindrical combustion chamber 114 and combustion gas generated by combustion in the latter is then discharged through the discharge port 116. At the same time fluid to be heated as identified by single line arrow marks is introduced into the apparatus by means of the blower 106 or the water pump 108 so that it is heated while it flows along the outer surface of the combustion chamber 114. Then, the heated fluid is discharged from the apparatus. The conventional apparatuses as described above are disclosed in Japanese Registered Pat. No. 226006 (Japanese Patent Publication No. 5116/1956).
The conventional apparatuses of the type of which rotational components are driven by means of a single motor have the following advantageous features.
(1) Since the driving means requiring electric power is constituted merely by a single motor, the apparatus can be manufactured at an inexpensive cost. PA1 (2) Rotational speed of a motor varies as voltage of electric power varies, because the rotational components as mentioned above are rotated at the same rotational speed by means of a single motor. Since flow rate of fuel and flow rate of combustion air vary in proportion to rotational speed, there is no fluctuation in ratio of combustion air to fuel irrespective of how the rotational speed of the motor varies. Therefore, the combustion state is not adversely affected. PA1 (3) As mentioned above, the amount of thermal energy generated by combustion varies without an occurrence of abnormal combustion due to fluctuation of voltage of electric current; however, the flow rate of fluid discharged from the blower or water feeding pump varies in proportion to variation of voltage of electric current. Therefore, fluctuation in temperature of fluid to be heated is avoided. PA1 (4) When the flow of fluid to be heated is stopped due to some trouble with the motor, supply of fuel is simultaneously interrupted and thereby combustion of fuel is stopped. Therefore, there is no fear of causing fire due to excessive heating of the apparatus. PA1 (5) The amount of thermal energy generated by combustion can be changed merely by changing the rotational speed of the motor. This is because of the fact that the ratio of combustion air to fuel does not vary and also the temperature of fluid to be heated does not vary for the reasons as mentioned in the foregoing paragraph (2). PA1 (1) When rotational speed is decreased to reduce the amount of thermal energy generated by combustion, in practice it is found that the temperature of the fluid to be heated is raised. PA1 (2) When rotational speed is decreased to reduce the amount of thermal energy generated by combustion, the combustion state deteriorates, resulting in the amount of generated smoke being increased. Further, when the apparatus continues to be operated for a long period of time while the amount of thermal energy generated by combustion is low, carbon tends to be deposited over the inner wall of the combustion chamber. Deterioration of the combustion state in that way is attributable mainly to the fact that the size of fuel grains distributed in the combustion chamber becomes larger as rotational speed of the fuel distributor decreases. Specifically, combustion in the combustion chamber of the apparatus is achieved in the form of divergent flame and therefore the apparatus does not always operate with a constant ratio of flow rate of combustion air to flow rate of fuel. For the reason that the range over which the amount of thermal energy generated by combustion can be reduced without any deterioration of combustion state while the rotational speed is low is limited to at least 80% as measured relative to the maximum amount of thermal energy generated by combustion, when it is determined that the generated thermal energy is lower than 80% of maximum, the apparatus should be operated only for a short period of time. PA1 (3) Piping is connected to inlet and outlet ports of the apparatus through which fluid to be heated is introduced and discharged. If this piping has high resistance against fluid flow, it causes the flow rate of fluid to be heated to decrease and the temperature increases abnormally. Accordingly, a decrease in the rotational speed of the motor to reduce the amount of thermal energy generated by combustion leads to a decrease in the flow rate of the fluid to be heated and an abnormal increase in the temperature of same. This means that there is no method of restoring the thus abnormally increased temperature to the initial normal level. PA1 (4) When atmosphere pressure is low, for instance, in the case when the motorcar or like vehicle moves in a mountain area, the flow rate of combustion air decreases and normal combustion in the apparatus is inhibited. However, there is no way of correctively bringing it to the normal combustion state.
In spite of the above-mentioned advantageous features of the conventional apparatus, the type adapted for introduction of combustion air from the combustion air blower 102 and that of fluid to be heated from the blower 106 or the water feeding pump 108 by changing rotational speed of a single motor 110 has the following problems.